1. Field of the Invention
Aspects of the present invention relate to a scanner, an image correction method therein and an image forming apparatus having the same.
2. Description of the Related Art
In a typical scanner, light is emitted from a light source to an object, such as a document placed on a transparent plate. The light is reflected from the document by a plurality of mirrors and is then focused on an image sensor by a focusing optical system. If a foreign substance is disposed between the document and the image sensor, it is difficult to acquire a high quality scan, due to noise generated by the foreign substance.
In order to reduce the influence of the foreign substance, a conventional method includes: acquiring a shading profile by scanning in a foreign substance detection mode; determining whether a foreign substance is detected with reference to a threshold value; and correcting noise generated due to the detected foreign substance, using an average filter. However, if the threshold is not appropriately applied, the presence of a foreign substance may be mistakenly detected, thereby causing difficulty in reducing the influence of the foreign substance.
Further, in the case that a foreign substance is disposed on a white testing patch formed on a transparent plate, even though a shading profile is acquired in a shifted acquired point, the influence of the foreign substance cannot be reduced. Furthermore, in the conventional method, it takes a long time to calculate a correction value, for an image region influenced by the foreign substance. In addition, the conventional method can determine only a position of the foreign substance in a sub-scan direction, that is, a direction perpendicular to a scan direction, in which a mirror, a focusing optical system and an image sensor move. The conventional method also cannot determine how far from the image sensor the foreign substance is, that is, the conventional method cannot determine the location of the foreign substance.